The present invention relates to a method for producing nuclear traces, or microholes originating from nuclear traces, of an individual ion or a countable number of ions in solid bodies by means of an accelerator, e.g. heavy ions in a heavy ion accelerator, with a defocused or attenuated beam and with elimination of the nonrequired particles.
The method proposed here relates to the production of the very finest individual holes in solid bodies and in particular organic foils, glasses and thin dielectric crystals. For certain purposes it is desired to produce holes of a heretofore unachieved smallness, i.e. with a hole diameter down to 0.01.mu., in a reproduceable manner. It is further desirable to have a ratio of hole diameter to hole length up to 1:1000.
Individual holes in foils can be produced by mechanical means with lasers, with electron beams, by means of photo or X-ray lithography, as well as with the aid of fiber bonding techniques. Moreover, it is known to produce a single hole membrane from unirradiated mica foils. In this case, one takes advantage of the fact that natural mica contains a few latent nuclear traces from the uranium which is contained therein in low concentration and undergoes spontaneous fission. After etching of the mica foils to expose the nuclear trace holes, a nuclear trace suitable for the desired hole is selected. The nonrequired nuclear trace holes, however, must subsequently be sealed off.
If one does not consider the other methods whose hole diameter to length ratio is a minimum of 1:100, only the nuclear trace technique makes it possible to produce holes smaller than 0.1.mu. with a hole diameter to length ratio down to 1:1000. The drawbacks in sealing all the other nuclear trace holes after searching out or selecting a single, suitably placed nuclear trace hole are as follows:
1. The size of the hole must be large enough to be made visible.
2. It is very difficult to localize individually placed holes which are smaller than 1.mu. in a light or electron microscope.
3. Micromanipulation is required to seal the remaining holes, for example, with an adhesive.
4. If one limits oneself to very thinly irradiated foils whose total surface contains only one hole on the statistical average, there arises the necessity, due to the statistical spread, of subjecting each individual foil to a quality control to determine whether 0.1 or 2 or 3 holes are present on the respective foil.
5. The hole cannot be placed into the center of the foil or at the most suitable spot on the foil in a directed manner.
6. It is impossible to simultaneously produce several foils each having a single hole.